Engineering a quieter leafblower

By November 1, 2018General, Noise Control, Quiet Design

COOL PROJECTS WHITE PAPER

Number:          001

Date:                  October 31, 2018

Title:                  Engineering a Quiet Leafblower

Result:               8 dBA reduction, rivaling best in class

Application Function Stage Methods Location
Products Initial Design Back of Napkin Optimize Client
Buildings Analysis Early Prototype Buy-Quiet 3rdParty
Industry Troubleshoot Late Prototype Source Control Test Lab
Research Test/Report Shipping Product Path Control Home Base

Blount International, makers of Oregon Outdoor Power products, had an ambitious goal to create a quieter leafblower.  The  battery-powered backpack leafblower should deliver more airflow than competitive products (including gas-powered blowers) yet have low noise levels and sound quality that is consistently preferred by respondents.  Prototypes of the OREGON BL120VX did not produce the desired results. Nelson Acoustics was retained to assist with noise-control design for a late engineering prototype.

Leafblower noise is evaluated in accordance with ANSI B175.2.  Sound pressure levels are averaged over 8 points around a 50’ radius circle on an unobstructed, mown grass surface .  The informal industry benchmark for leafblower noise is 65 dBA SPL.

First, an improvised outdoor range was established at the client’s site, which unavoidably included a hard surface, reflectors, and obstructions.  Nelson Acoustics developed correction factors to “calibrate” the results for comparison with what would be expected in a B175.2 test.

Next, we measured Blount’s engineering Prototype and five competitive units.  The Prototype met the airflow goals but came in loudest at 67 dBA.  Analysis showed that this was due in large part to the prodigious airflow.  After all, more airflow comes from more power, and more power (all things being equal) creates more noise.  A focal point of Nelson Acoustics’ work, however, is to find ways to reduce noise without sacrificing performance.

I analyzed the relative contributions of different components and/or sound paths.  Recommendations were provided to optimize the blower and to introduce noise control elements.  Blount’s engineer made several stunningly rapid field modifications to implement the proposed “path” noise control modifications.

Two days and several modification cycles later, the unit was down to 60 dBA without significant change in airflow, battery life, or weight.  The perceived loudness had been reduced by 30% and the perceived tonality had dropped by 35%.

The recommended blower modifications were explored by the fan vendor and incorporated into the final product.

Nelson Acoustics later measured the final shipping version of the BL120VX at 59 dBA (full throttle, continuous operation) and 57 dBA in optional “stealth mode”.  The previous “best in class” competitor unit, which sustains similar airflows only in temporary “boost” mode, rated 58 dBA.

For what it’s worth, Fluffy the skittish barn cat sat perfectly still and observed most of the final test from the edge of the 50’ circle.

The Oregon BL120VX proves that powerful doesn’t have to be noisy and quiet doesn’t necessarily mean weak, as long as you’re willing to do things a bit differently. Let Nelson Acoustics help you integrate “intrinsically quiet design” principles into your next product design.

See https://www.oregonproducts.com/bl120vxbackpackblower

Video at https://youtu.be/ti0gV2oq9HY.

To get more information on Nelson Acoustics’ low-noise design services, http://nelsonacoustical.com/low-noise-design/

Or simply contact Nelson Acoustics at http://nelsonacoustical.com/contact/

 

Nelson Acoustics

David Nelson, INCE Bd. Cert.

Principal Consultant

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